The invention relates to active principle carriers based on non-ionic surfactants and their applications notably in food, cosmetic and pharmaceutical fields.
The invention also relates to compositions in which at least one active principle is encapsulated within this carrier, in particular compositions for use as food, cosmetics or pharmaceuticals and their method of manufacture.
It is known that there is a significant necessity, in these fields, to protect a certain number of fragile or volatile molecules or to regulate the conditions of their release into an external medium.
One of the techniques which enables attaining such an aim is the microencapsulation of active molecules. The aim of this encapsulation is to reduce the evaporation and the transfer towards the environment of the active material, either during storage or during the development of the products, or even during their consumption.
The invention can also enable rendering the material easier to use by diluting it and by favouring its homogeneous distribution within the support.
The list of sensitive materials is long. Amongst the most used, acids, for example ascorbic acid or lactic acid, colouring agents, for meats in particular, lipids, vitamins, flavours and essential oils, enzymes, will be cited for example in the food field.
In the cosmetic or pharmaceutical field, dihydroxyacetone, vitamins, phenolic oligomers, biomolecules, can be cited. Some of the active products cited in foods are also useful in cosmetics or in pharmaceuticals.
The technologies, currently used in order to attain this object rely on the use of polymers. These are techniques either of coacervation, extrusion or coating by fluidised bed.
Apart from the dispersing effect, the surfactant molecules enable, in certain cases, protecting and vectorising and then releasing the active molecules in a controlled manner using microcapsules formed by a supramolecular combination of surfactant molecules. The most common example is that of liposomes used in cosmetics and in the biomedical field. These liposomes correspond to an arrangement of unilamellar or multilamellar vesicles of sizes between a few hundred Angstroms and several microns. These vesicles are, in the case of liposomes, obtained from phospholipidic molecules (extracted for example from soya or egg). These liposomes are capable of encapsulating hydrophilic or even lipophilic active molecules and thus carrying out the functions of vectoring and release sought after.
The classical methods of preparation of the liposomes most often necessitate the presence of an organic co-solvent or alcohols, products which are strongly advised against for applications in the field of food and which are to be prevented in the other fields more particularly covered by the present invention.
However, in the field of the food industry, tests carried out with lecithins, in particular in the form of liposomes, have shown the technological limitations of this technique. The use of liposomes in the food industry is in fact limited by the process of manufacture which has a certain number of technical problems. More specifically, the use of liposomes in the food industry has the drawback of leading to a low yield of encapsulation and this despite a relatively heavy and therefore expensive technology to carry out.
The U.S. Pat. No. 4,217,344 describes a process which enables producing a dispersion of spheres which comprises an arrangement of molecular layers encapsulating an aqueous phase. The process described in this document consists in mixing a water-dispersible lipid compound with the aqueous phase to be encapsulated, the lipophilic/hydrophilic ratio of the lipid compound being such that the liquid swells in the aqueous phase to form a lamellar phase which is then submitted to a stirring step.
Amongst the lipid compounds cited in this document, compounds are found essentially of the polyglycerol ether type synthesised specifically for forming vesicles.
A novel family of surfactants of the ether type has now been found which enables obtaining stable vesicles which allow encapsulating active principles.
A more particular advantage of the surfactants selected according to the invention is that they are natural, biodegradable non-ethoxylated products which are easily obtained commercially and which thus enable obtaining multilamellar microvesicles from commercial surfactants, without having to carry out a particular synthesis.
The liposomes or other lipid vesicles described in the literature are in fact hitherto based essentially on surfactants:
--ionic or zwitterionic surfactants, as is the case of lecithin and its derivatives, or sodium dodecylsulphate (SDS),
--non-ionic ethoxylated surfactants, as is the case of sorbitan ester-based microcapsules,
--non-ionic surfactants specially synthesised to give vesicles.
The use of these products has certain drawbacks, amongst others, in the fields of cosmetics and food:
--irritation in the case of ionic surfactants and certain non-ionic ethoxylated surfactants,
--risk of allergy due to the traces of ethylene oxide in the ethoxylated products,
--great sensitivity to microbial contamination as far as lecithin and ethoxylated products which inhibit preservatives are concerned,
--chemical instability as far as lecithin is concerned,
--specificity of formulation.